1. Field of the Invention
This invention relates to the production of an alkali metal sulfate and HCl by use of an alkali metal fluosilicate as an intermediate reactant in a process for the production of certain useful products. More particularly, the invention relates to a process for the production of an alkali metal sulfate and hydrochloric acid and ultimately of anhydrous hydrogen chloride wherein an alkali metal fluosilicate is employed as a key intermediate reactant.
2. Description of the Prior Art
In the acidulation of fluoride-containing phosphate rock to form materials useful in fertilizers, an alkali metal fluosilicate is often produced as a by-product. The fluosilicate is formed in a process such as that set forth in U.S. Pat. No. 4,055,626, which controls the emission of fluoride-containing gases. This fluosilicate contains useful ions and is of interest in the recovery of valuable products therefrom.
Processes utilizing an alkali metal fluosilicate as a reactant are known. These processes include the use of alkali metal fluosilicates to form potassium sulfate, a commercially useful product. Exemplary of these prior art processes are U.S. Pat. No. 1,054,518 to Doremus and U.S. Pat. No. 3,082,061 to Barry et al. Although both patents generally disclose potassium sulfate formation from potassium fluosilicate by reaction with sulfuric acid, they do not contemplate a reaction sequence which produces hydrochloric acid from the fluosilicate by making use of HF and SiF.sub.4 reaction by-products in a novel reaction.
Although it is known in the prior art to form hydrochloric acid from H.sub.2 SiF.sub.6, the prior art of which we are aware does not use an alkali metal fluosilicate as a reacting material, that is, as the source of H.sub.2 SiF.sub.6, in the production of hydrochloric acid. Exemplary of these prior art processes are U.S. Pat. No. 3,021,193 to Cunningham and U.S. Pat. No. 3,369,863 to Jones et al. Further, these patents do not contemplate the discovery of applicants for the production of hydrochloric acid from which anhydrous HCl may be recovered.
In U.S. Pat. No. 4,137,063, filed June 24, 1977, in which one of us is an inventor, there is disclosed a process for production of a solid potassium polyphosphate polymer which comprises reacting potassium fluosilicate with a mixture of phosphoric acid and sulfuric acid. The reaction is continued for a sufficient period of time to evolve fluorides in the form of SiF.sub.4 and HF. It is a feature of that process that these fluorides may be reacted with a potassium salt such as KCl to form additional potassium fluosilicate which is reused in the process. Also recovered from this latter reaction is KCl and HCl in an aqueous solution from which the HCl may be recovered.
While certain of the reactions of U.S. Pat. No. 4,137,063 are related to the process of this invention, there is not any disclosure in U.S. Pat. No. 4,137,063 for the production of alkali metal sulfate in quantity, together with anhydrous HCl, which are valuable products resulting from the instant process.